A large Late Cretaceous PACHYCEPHALOSAUR. This dionsaur had a plate of bone 9 inches (23 cm) thick covering its BRAIN. Wartlike knobs and 5-inch (13-cm) spikes fringed this dome and decorated the dinosaurs small nose. This BIPEDAL plant eater is known only from skulls found in Wyoming and Alberta, Canada. These skulls were 26 inches (66 cm) long, three times as large as the skull of STEGOCERAS. If the rest of Pachycephalosaurus's body was in proportion to its skull, it was 15 feet (4.6 m) long. The largest of the pachycephalosaurs.